– Small Bowel

  Small intestine – nutrient and water absorption


  Large intestine – water absorption


  Duodenum


•  Bulb (1st portion) – 90% of ulcers here


•  Descending (2nd) – contains ampulla of Vater (duct of Wirsung) and duct of Santorini


•  Transverse (3rd)


•  Ascending (4th)


•  Descending and transverse portions are retroperitoneal


•  3rd and 4th portions – transition point at the acute angle between the aorta (posterior) and SMA (anterior)


•  Vascular supply is superior (off gastroduodenal artery) and inferior (off SMA) pancreaticoduodenal arteries


  Both have anterior and posterior branches


  Many communications between these arteries



  Jejunum


•  100 cm long; long vasa recta, circular muscle folds


•  Is the maximum site of all absorption except for B12 (terminal ileum), bile acids (ileum – non-conjugated; terminal ileum – conjugated), iron (duodenum), and folate (terminal ileum)


•  95% of NaCl absorbed and 90% of water absorbed in jejunum


•  Vascular supply – SMA


  Ileum – 150 cm long; short vasa recta, flat


•  Vascular supply – SMA


  Intestinal brush border – maltase, sucrase, limit dextrinase, lactase


  Normal sizes – small bowel/transverse colon/cecum → 3/6/9 cm


  SMA eventually branches into the ileocolic artery


  Cell types


•  Absorptive cells


•  Goblet cells (mucin secretion)


•  Paneth cells (secretory granules, enzymes)


•  Enterochromaffin cells (APUD, 5-hydoxytryptamine release, carcinoid precursor)


•  Brunner’s glands (alkaline solution)


•  Peyer’s patches (lymphoid tissue); increased in the ileum


•  M cells – antigen-presenting cells in intestinal wall


  IgA – released into gut; also in mother’s milk


  Fe – small bowel has both heme and Fe transporters


  Migrating motor complex (gut motility)


•  Phase I – rest


•  Phase II – acceleration and gallbladder contraction


•  Phase III – peristalsis


•  Phase IV – deceleration


•  Motilin is most important hormone in migrating motor complex (acts on phase III)


  Bile salts (acids)


•  95% of bile salts are reabsorbed


  50% passive absorption (non-conjugated bile salts) – 45% ileum, 5% colon


  50% active resorption (conjugated bile salts) in terminal ileum (Na/K ATPase); conjugated bile salts are absorbed only in the terminal ileum


•  Gallstones form after terminal ileum resection from malabsorption of bile salts


SHORT-GUT SYNDROME


  Diagnosis is made on symptoms, not length of bowel


  Symptoms: diarrhea, steatorrhea, weight loss, nutritional deficiency


  Lose fat, B12, electrolytes, water


  Sudan red stain – checks for fecal fat


  Schilling test – checks for B12 absorption (radiolabeled B12 in urine)


  Probably need at least 75 cm to survive off TPN; 50 cm with competent ileocecal valve


  Tx: restrict fat, PPI to reduce acid, Lomotil (diphenoxylate and atropine)


CAUSES OF STEATORRHEA


  Gastric hypersecretion of acid → ↓ pH → ↑ intestinal motility; interferes with fat absorption


  Interruption of bile salt resorption (eg terminal ileum resection) interferes with micelle formation and fat absorption


  Tx: control diarrhea (Lomotil); ↓ oral intake, especially fats; Pancrease, PPI


NONHEALING FISTULA


  “FRIENDS” – mnemonic for causes of nonhealing fistula: foreign body, radiation, inflammatory bowel disease, epithelialization, neoplasm, distal obstruction, sepsis/infection


  High-output fistulas are more likely with proximal bowel (duodenum or proximal jejunum) and are less likely to close with conservative management


  Colonic fistulas are more likely to close than those in small bowel


  Patients with persistent fever – need to check for abscess (fistulogram, abdominal CT, upper GI with small bowel follow-through)


  Most fistulas are iatrogenic and treated conservatively 1st → NPO, TPN, skin protection (stoma appliance), octreotide


  Majority close spontaneously without surgery


  Surgical options: resect bowel segment containing fistula and perform primary anastomosis


OBSTRUCTION


  Without previous surgery (most common)


•  Small bowel – hernia


•  Large bowel – cancer


  With previous surgery (most common)


•  Small bowel – adhesions


•  Large bowel – cancer



  Symptoms: nausea and vomiting, crampy abdominal pain, failure to pass gas or stool


  Abdominal x-ray: air–fluid level, distended loops of small bowel, distal decompression



  3rd spacing of fluid into bowel lumen occurs – need aggressive fluid resuscitation


  Air with bowel obstruction – from swallowed nitrogen


  Tx: bowel rest, NG tube, IV fluids → cures 80% of partial SBO, 40% of complete SBO


  Surgical indications: progressing pain, peritoneal signs, fever, increasing WBCs, (all signs of strangulation or perforation), or failure to resolve


GALLSTONE ILEUS


  Small bowel obstruction from gallstone usually in the terminal ileum


  Classically see air in the biliary tree in a patient with small bowel obstruction


  Caused by a fistula between the gallbladder and second portion of duodenum


  Tx: remove stone from terminal ileum


•  Can leave gallbladder and fistula if patient too sick


•  If not too sick, perform cholecystectomy and close duodenum


MECKEL’S DIVERTICULUM


  2 ft from ileocecal valve; 2% of population; usually presents in 1st 2 years of life with bleeding; is a true diverticulum


  Caused by failure of closure of the omphalomesenteric duct


  Accounts for 50% of all painless lower GI bleeds in children < 2 years


  Pancreas tissue – most common tissue found in Meckel’s (can cause diverticulitis)


  Gastric mucosa – most likely to be symptomatic (bleeding most common)


  Obstruction – most common presentation in adults


  Incidental → usually not removed unless gastric mucosa suspected (diverticulum feels thick) or has a very narrow neck


  Dx: can get a Meckel’s scan (99Tc) if having trouble localizing (mucosa lights up)


  Tx: diverticulectomy for uncomplicated diverticulitis or bleeding


•  Need segmental resection for complicated diverticulitis (eg perforation), neck > ⅓ the diameter of the normal bowel lumen, or if diverticulitis involves the base


DUODENAL DIVERTICULA


  Need to rule out gallbladder-duodenal fistula


  Observe unless perforated, bleeding, causing obstruction, or highly symptomatic


  Frequency of diverticula: duodenal > jejunal > ileal


  Tx: segmental resection if symptomatic


•  If juxta-ampullary usually can’t get resection and need choledochojejunostomy for biliary or ERCP with stent for pancreatitis symptoms (avoid Whipple here)


CROHN’S DISEASE


  Inflammatory bowel disease causing intermittent abdominal pain, diarrhea, and weight loss; can also cause bowel obstructions and fistulas


  15–35 years old at 1st presentation; in Ashkenazi Jews


  Extraintestinal manifestations – arthritis, arthralgias, pyoderma gangrenosum, erythema nodosum, ocular diseases, growth failure, megaloblastic anemia from folate and vitamin B12 malabsorption


  Can occur anywhere from mouth to anus; usually spares rectum


  Terminal ileum – most commonly involved bowel segment


  Anal/perianal disease – 1st presentation in 5%


•  Tx: Flagyl


•  Anal disease most common symptom – large skin tags


  Most common sites for initial presentation


•  Terminal ileum and cecum – 40%


•  Colon only – 35%


•  Small bowel only – 20%


•  Perianal – 5%


  Dx: colonoscopy with biopsies and enteroclysis can help make the diagnosis


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Jun 24, 2017 | Posted by in GENERAL SURGERY | Comments Off on – Small Bowel

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